The invention relates to a magnetic coupling, in particular a magnetic coupling pump, which comprises an inner rotor and an outer rotor which each carry magnets, between which a double-wall containment shroud is disposed, which comprises an outer shroud and an inner shroud, which each comprise a flange, a middle section and a bottom section, wherein a gap is disposed between the middle section and the bottom section, and wherein the inner shroud is connected by its flange to the flange of the outer shroud.
Magnetic coupling pumps are generally known, and described for example in DE 10 2009 022 916 A1. The pump output is transmitted from a drive shaft via a magnet-carrying rotor (outer rotor) contactless and essentially slip-free to the pump-side magnet carrier (inner rotor). The inner rotor drives the pump shaft, which is mounted in a sliding bearing lubricated by the conveying medium, i.e. in a hydrodynamic sliding bearing. The containment shroud with its cylindrical wall lies between the outer rotor and the inner rotor, i.e. between the outer and inner magnets. The containment shroud is connected with its flange to a pump component, for example a housing cover, and opposite thereto comprises a closed base. The containment shroud, i.e. the magnetic coupling pump, reliably separates the product space from the surroundings, so that the risk of a product escaping with all the associated unfavorable consequences can be excluded. A magnetic coupling pump is accordingly the combination of conventional pump hydraulics with a magnetic drive system. This system uses the forces of attraction and repulsion between magnets in the two coupling halves for the contactless and slip-free torque transmission. The containment shroud, which separates the product space and the surroundings from one another, is located between the two rotors provided with magnets. The magnetic coupling pump therefore offers great advantages especially when dealing with very valuable or very dangerous substances.
Containment shrouds can be made from various materials, such as for example metals of the most diverse alloy compositions, plastics or ceramics. Containment shrouds made of metal disadvantageously cause eddy current losses, plastic containment shrouds having only a limited resistance to temperature and pressure, which is particularly disadvantageous in the case of high medium temperatures and/or high pump pressures. To that extent, ceramic containment shrouds have become established in practice, containment shrouds made of glass (DE 10 2009 022 916 A1) having also become known recently.
Centrifugal pumps with a magnetic coupling, i.e. magnetic coupling pumps according to DIN EN ISO 2858 and DIN EN ISO 15783 and according to API 685, are equipped with single-wall containment shrouds in the standard, i.e. in a known manner. The containment shroud separates the product space in a leakage-free manner from the atmosphere and forms the static seal between the inner and outer magnetic rotor. In the cylindrical part, i.e. in its middle section, the containment shroud usually has a wall thickness of 1-2 mm. Damage to the containment shroud due to roller bearing damage on the outer magnetic rotor or sliding bearing damage in the region of the inner magnetic rotor can lead to the escape of conveying liquid into the atmosphere space of the intermediate skirt. In order to prevent an escape of conveying liquid, use is made of double-wall containment shrouds, amongst other things when pumping hazardous (e.g. toxic, carcinogenic, aggressive) conveying liquids.
Double-wall containment shrouds are known for example from EP 0 286 822 B1, but also from EP 0268 015. A double-wall containment shroud is known from EP 1 777 414 A1, the inner shroud and outer shroud whereof make contact with one another at least in the region of the cylindrical lateral surface, wherein a path network is constituted in this contact zone, in which path network there is disposed a liquid medium, i.e. a medium of sufficient viscosity, such as for example liquids or pasty materials, for example a heat-conducting oil.
Magnetic power losses of 10-15% have to be accepted when use is made of single-wall containment shrouds. This value can double when use is made of double-wall containment shrouds. For system-related reasons, the magnetic power losses are converted into heat in the case of metallic containment shrouds, said heat being discharged via the conveying product. For design-related reasons, however, the heat arising at the outer containment shroud cannot be completely discharged to the atmosphere. It is important here to discharge the heat between the outer and inner containment shroud due to the air-filled or evacuated intermediate space via heat-conducting products into the conveying product. The use of heat transfer oils or heat-conducting paste is known here. The main drawback here can be considered to be, for example, damage to the outer containment shroud with a corresponding escape of heat-conducting liquids or pastes from the intermediate space of the containment shrouds into the atmosphere with the risk of ignition or damage to the inner containment shroud due to incompatibility of the heat-conducting liquid paste with the conveying product, so that the latter is unusable on account of contamination. It is also a drawback, however, that special sealing measures, especially in the region of the abutting flanges of the outer and inner shroud, have to be taken, so that an escape of the liquid or paste introduced into the gap, even when the double-wall containment shroud is intact, is avoided. Additional sealing measures, however, mean additional cost, as well as the additional use of material. Furthermore, the special sealing also involves additional potential hazard, because the sealing measure can also fail, so that there is the risk of a shut-down, although the inner shroud and the outer shroud are actually still intact. Especially in the case of an inspection, in which the double-wall containment shroud possibly also has to be dismantled for control purposes, every effort has to be made to ensure that the liquid present does not get into the surroundings.